As the Great War increased in both length and scale, it became obvious to the Admiralty that their destroyer flotillas must be relieved of some of their less arduous workload so that their real value could be better exploited. Thus were born the P-boats, or more correctly the "P" class patrol boats, which were to become such a useful adjunct to so many operations throughout the War. Intended for routine patrol and escort duties as well as submarine detection, all were built under the Emergency War Programme and their outline design specified minimum size consistent with sea-keeping qualities, simplicity of construction, economy of fuel, and adequate speed to run-down submarines. Built of mild steel but with a hardened steel stem for ramming U-boats, they were given large rudders to facilitate rapid turning. Displacing 613 tons, each measured 230 feet in length with a 23¾ foot beam, and had turbine powered twin screws to give a top speed of 20 knots. Designed to mount 2-4in. guns, only P-52 actually carried this armament with all the others having only 1-4in. gun, 1-2pdr. pom-pom and 2 single 14in. torpedo tubes removed from old torpedo boats.
The first vessels were completed late in 1915 and production continued with modified pc-boats until 1918. Even though 37 P-boats were built in all, only two were lost in action, the remainder all ending their days with the shipbreakers. P-40 was eventually broken up at Milford Haven in 1928.